01 -
Preheat oven to 375°F. Lightly grease a 9x13 inch baking dish with butter.
02 -
Melt butter in a medium saucepan over medium heat. Stir in garlic and cook just until fragrant, about 1 minute. Add flour and stir constantly for 2 minutes to create a smooth, pale roux.
03 -
Lower heat to medium-low. Gradually whisk in milk, adding it slowly and whisking continuously to prevent lumps. Cook until the sauce thickens and coats the back of a spoon, about 5 minutes.
04 -
Stir in chicken bouillon or kosher salt, additional salt, and black pepper. Remove the pan from heat once the sauce is velvety and smooth.
05 -
Arrange half of the sliced potatoes evenly in the prepared baking dish.
06 -
Pour over half of the prepared cream sauce, spreading to cover potatoes. Sprinkle half of the mozzarella and half of the Parmesan cheese over the layer.
07 -
Arrange remaining potato slices on top. Pour over the rest of the cream sauce. Finish with remaining mozzarella and Parmesan cheese.
08 -
Cover dish tightly with aluminum foil. Bake for 40 minutes to soften the potatoes.
09 -
Remove foil and bake uncovered for 30 minutes, or until the top is bubbling and golden. For extra crispness, broil for 1-2 minutes, watching attentively so the top does not burn.
10 -
Scatter fresh chives across the top and serve hot directly from the oven.